Control flaps are used for changing the shape of a wing, which affects the lift and direction of an aircraft. Conventional control flaps are manufactured using rigid parts. Fluid flow over the surfaces of the wing and the flaps is less than optimal aerodynamically over the full range of motion of these rigid control flaps. The load distribution over such rigid control flaps is not favorable, because large local stresses are located at the points of connection between the wing and the control flaps.
Depending on context the term flexible may mean adaptable, variable, capable of change or pliable. Flexible is used in its broadest reasonable definition within context.